1. Field of the Invention
The present invention relates to an optical network unit ONU linking a multi-functional common unit board installed in a shelf, and to a service unit board for a multiple digital subscriber line xDSL and for a plain old telephone service POTS through a common bus.
2. Description of the Related Art
Recently, according to the variety of data communication services and explosive increases in the demands of data communication services, subscribers accustomed to the data transmission of low and middle speeds, such as voice data transmission, are beginning to request a wide area network WAN capable of providing a high-speed digital data transmission service, such as multimedia data transmissions.
Therefore, many technologies have been developed to provide such a high speed digital data service. Two standards capable of providing a high-speed digital data transmission service among the developed technologies are a fiber to the curb (FTTC) technology and a fiber to the home (FTTH) technology.
The FTTC technology is applied when optical fiber cables are installed from a public network to the front door of each home of the subscribers. In this case, the curbs are located in each of the densely inhabited districts of the subscribers respectively, and optical transmissions are performed through the optical fiber cables from a switching apparatus in the public network to the curbs. Furthermore, data is transmitted through conventional telephone lines from the curb to each of the corresponding subscribers.
On the other hand, the FTTH technology sets the curb inside each home of the subscribers, respectively.
A fiber loop carrier-curb FLC-C system for embodying the above described FTTC technology receives WAN data, such as a digital service level 1 DS1 of 1.544 Mbps (megabits per second), a digital service 1 Europe DS1E of 2.048 Mbps, a digital service level 3 DS3 of 51.48 Mbps, an integrated service digital network ISDN, or 10 Base_T, or vice versa. Moreover, the FLC-C system performs a synchronous optical transmission, such as a synchronous transfer level-1 STM-1 or a synchronous transfer level-4 STM-4, and inverse-multiplexes the WAN data to be transmitted to the subscriber, or vice versa.
A network configuration in the conventional FLC-C system generally includes a host digital terminal HDT, and multiple optical network units ONUs. Normally, the HDT is installed in a main body for managing and controlling the FLC-C system, such as a central office CO, and the ONU is installed in densely inhabited districts of subscribers, such as multiple curbs.
The HDT is connected into a public switched telephone network PSTN or an asynchronous transfer mode ATM. After receiving the data through the PSTN or the ATM network, the HDT performs a synchronous optical transmission to the ONU, or vice versa. The ONU inverse-multiplexes the optical data signal transmitted from the HDT, and provides a high speed asynchronous transmission channel having a download speed of 1.5˜6 Mbps (or 2˜8 Mbps in E1) and an upload speed of 16˜24 Kbps (kilobits per second) for each of the subscribers through a telephone line, or vice versa.
As described in the above statement, the ONU is one of the subscriber control units for providing an interface and a concentration function in data transmissions for the subscribers, while a backbone network includes the HDT (sometimes, the ONU is connected into a digital subscriber line access multiplexor DSLAM instead of directly connecting to the HDT). Furthermore, because so many ONUs have to be installed for the FLC-C system, economical efficiency is one of the most important factors to be considered.
As a preceding technology, the article, “600 Mbps 150 Mbps Asymmetric ATM-PDS Transmission Equipment for ATM Video Service and ISD”, in Technical Report of IEICE Vol. No CS97-29 by Hiroshi Ichibangase discloses a subscriber control unit including an optical signal processor and a packet driver specification PDS for connecting to a public network, an ATM multiplexor, an ATM cell assembler, and a subscriber interface terminal for connecting a cable TV (television) CATV and for transmitting a video data. In this article, the subscriber control unit provides standard functions such as an ATM multiplexor and an ATM cell assembler for performing ATM cell functions.
Further, the article, “Instant Transfer of Huge Contents on an Optical Subscriber Network”, in Technical Report of IEICE Vol. No CS96-33 by Tara Yoshikawa discloses a subscriber control unit including a function unit, such as an ATM physical interface ATM-PHY, for connecting a public network. In this article, the subscriber control unit provides various kinds of customer premises network CPN including a digital signal processor DSP, a field programmable gate array FPGA, and so on. These units transmit data through a common bus.
The subscriber control unit described in the above articles, focuses only on economical efficiency so that the ONU can perform minimum functions. On the contrary, the recent trends in development of WAN data services request a network unit with high speed and large capacity, such as an interactive service based on multimedia, for numerous subscribers. Therefore, it is required to develop an inexpensive ONU with high speed and large capacity.
In other words, it is required to develop an ONU having flexibility and expandability according to densely inhabited districts of the subscribers and requested speed degrees of data services, while the ONU keeps economical efficiency.